Yucca Mountain is a barren desert ridge about 90 mi (161 km) northwest of Las Vegas, Nevada. The U.S. Department of Energy plans to build its first high-level nuclear waste storage facility there in an extensive series of tunnels deep beneath the desert surface. Choosing this site has been a long and divisive process. Although over 20 years and more than $7 billion have been spent designing and testing the storage facility, scientists are still not clear whether the facility will remain dry and stable for the thousands of years it will take for natural decay processes to make the wastes less radioactive.
Most of the nuclear waste to be stored at Yucca Mountain will come from nuclear power plants . As radioactive uranium 235 is consumed in fission reactions, the fuel becomes depleted and accumulating waste products reduce energy production. Every year about one-third of the fuel in a typical reactor must be removed and replaced with a fresh supply. The spent (depleted) fuel must be handled and stored very carefully because it contains high concentrations of dangerous radioactive elements, in addition to natural uranium, thorium, and radon isotopes. Some of these materials have very long half-lives, requiring storage for at least 10,000 years before their radioactivity is reduced to harmless levels by natural decay processes.
Originally, the United States intended to reprocess spent fuel to extract and purify unused uranium and plutonium as fuel for advanced breeder reactors (a type of nuclear reactor). Reprocessing plants released unacceptable amounts of radioactivity, however, and breeder reactors proved to be too expensive and dangerous to serve as civilian power sources. For a time in the 1950s, nuclear wastes were dumped in the ocean, but that practice was stopped when it was discovered that the corroding metal waste containers allow radio-isotopes to dissolve in seawater.
In 1982, the U.S. Congress ordered the Department of Energy (DOE) to build two sites for permanent radioactive waste disposal on land by 1998. Understandably, no one wanted this toxic material in their backyard. In 1987, after a long and highly contentious process, the DOE announced that it could only find one acceptable site: Yucca Mountain.
The storage facility would be a honeycomb of tunnels more than 1,000 ft (303.3 m) below ground. When finished, the total length of the tunnels would be more than 112 mi (180 km)—approximately the size of the world's largest subway system in New York City. Altogether, the tunnels would have room for more than 80,000 tons of nuclear waste packed in corrosion-resistant metal canisters. Because Yucca Mountain is located in one of the driest areas in the United States, and the bedrock is composed of highly stable volcanic tuff (compacted ash), the DOE hopes that storage areas will remain intact and free of leaks for the thousands of years it will take for the wastes to decay to a harmless state. Total costs for this facility have been estimated to be as high as $58 billion for construction and the first 50 years operation.
Ever since its designation as the nation's sole repository for high-level nuclear waste, Yucca Mountain has been embroiled in both scientific and political controversy. Citizens of Nevada feel that their state was chosen only because they don't have the political clout to resist. Ironically, Nevada doesn't have a nuclear power plant. State officials and the Nevada Congressional delegation have vowed to do everything in their power to try to stop construction and operation of the nuclear waste facility.
Scientists are divided about the safety of the site. Although some studies suggest that Yucca Mountain has been geologically stable for thousands of years, others show a history of fairly recent volcanic activity and large earthquakes in the area. Fractures and faults have been discovered in the bedrock that could allow ground water to seep into storage vaults if the climate changes. One hydrologist suggested that groundwater levels, while low now, could rise suddenly and fill the tunnels with water. Opponents of the site claim that over 200 technical problems had not been solved by the DOE by 2002.
The storage project has been continually delayed. After over $1 billion had been spent on exploratory studies and trial drilling at Yucca Mountain, the DOE announced in 1986 that it could not meet the 1998 deadline imposed by Congress. The earliest date by which the repository might be operational is now 2010. States and power companies, having already paid more than $12 billion to the DOE to build the repository, have threatened to sue the government if it does not open as originally promised. Some utilities have begun to negotiate privately with Native American tribes and foreign countries to take their nuclear wastes.
While underground storage of nuclear wastes is fraught with problems and uncertainties, none of the alternatives now available appears better. Currently, about 45,000 tons of spent fuel is sitting at 131 sites, including 103 operating nuclear plants, in 39 states. Another 20,000 tons are expected to be generated before a storage facility can be opened in 2010, or about 2,000 tons of new waste per year. Most of this waste is being stored in deep water-filled pools inside nuclear plants. These pools were never intended for long-term storage and are now over-crowded. Many power plants have no more room for spent fuel storage and will be forced to shut down by 2010 unless some form of long-term storage is approved. In 1997, the DOE asked Congress for $100 million to purchase large steel casks in which power companies can stockpile spent fuel assemblies in outdoor storage yards. Neighbors who live near these storage sites worry about the possibility of leakage and accidents. Nevertheless, several utilities have already begun on-site dry cask storage . It is estimated that 165 million Americans live within a two-hour drive of stored high-level nuclear waste.
In February 2002, under the recommendation of Energy Secretary Spencer Abraham, President George W. Bush approved Yucca Mountain as the nation's nuclear waste storage site, to be opened in 2010. It would receive a minimum of 3,000 tons of nuclear waste per year for 23 years, storing up to a legal maximum of 77,000 tons. After 2007, another energy secretary may consider expanding the storage facility.
As expected, and as allowed by federal law, the state of Nevada filed a formal objection to the site approval. In May 2002 the U.S. House of Representatives voted to override Nevada's objections to the site. A major political battle was then taken to the U.S. Senate, which had until July 26, 2002 to decide upon the future of U.S. nuclear waste disposal. In July 2002 the site was approved.
The nuclear power industry is the main supporter of the storage site, in order to continue producing nuclear energy, which supplies about 20% of U.S. electricity. Opponents of the site claim that long-term storage and transportation of the waste is far too dangerous, given inconclusive scientific studies. Furthermore, if nuclear power is continued, opponents note that Yucca Mountain will eventually run out of space and the nuclear waste problem will still be unsolved.
Waste storage at Yucca Mountain is a complex, expensive, and potentially high-risk problem that exemplifies the complications of many environmental issues. It also demonstrates the difficulty of making democratic decisions in issues with consequences that affect large geographical areas and future generations in ways that are difficult to predict and potentially control.
[William P. Cunningham Ph.D. and Douglas Dupler ]
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U.S. Department of Energy, 1000 Independence Avenue SW, Washington, DC 20585 (202) 586-6151, Fax: (202) 586-0956, <http://www.doe.gov>
Yucca Mountain Project, PO Box 364629, North Las Vegas, NV 89036-8629 (800) 225-6972, Fax: (702) 295-5222, <http://www.ymp.gov>
The United States has accumulated more than forty thousand tons of spent nuclear fuel and high-level radioactive wastes from commercial, research, and defense activities with an estimated two thousand tons added every year. The materials are currently stored in thirty-nine states at 131 temporary aboveground facilities, requiring constant monitoring and maintenance. Worldwide, scientific consensus holds that deep geologic disposal, with robust engineered barriers, can best contain and isolate these materials from the accessible environment. The Nuclear Waste Policy Act of 1982 established this approach as U.S. policy. If ultimately licensed by the Nuclear Regulatory Commission, Yucca Mountain, in southern Nevada, could become the first U.S. geologic repository for such materials. The Department of Energy (DOE) plans to open the proposed repository by 2010 if a license is granted.
Between about fifteen and twelve million years ago, large volcanic eruptions deposited hot ash that solidified into the rock composing Yucca Mountain. The proposed repository would be built about one thousand feet underground and, on average, about one thousand feet above the water table in rock that has remained undisturbed for millions of years. For about two thousand feet under the mountain's surface the rock is very dry, or unsaturated, meaning its pore spaces are not completely filled with water.
Waste Forms and Other Engineered Barriers
All materials sent to a repository would be in solid form. Spent nuclear fuel comprises hard ceramic pellets in sealed corrosion-resistant metal tubes. Liquid wastes from defense-related activities would be solidified into glass logs, inside sealed metal containers, before shipment.
At the repository, the materials would be sealed inside double-walled containers, called waste packages, made of stainless steel and a corrosion-resistant alloy. Once underground, each waste package would be placed on its own individual pallet, in one of dozens of miles of tunnels carved deep within the rock. In addition, corrosion-resistant titanium drip shields would be placed above the sealed containers as an added barrier to water. (See illustration.)
Potential Problems at Site
Groundwater contamination. Yucca Mountain's climate is very dry, with annual precipitation averaging about 7.5 inches (190 millimeters or mm). About 95 percent either runs off, evaporates, or is taken up by vegetation. Overall, very little water infiltrates the mountain and reaches the repository level. The bulk of any water moves very slowly through the unsaturated rock. Some data, however, suggest that water may reach the repository level in a few decades by moving through fractures that are large enough to permit this. Therefore, the sophisticated computer calculations used to estimate the repository's likely performance assume the presence of such fractures and their impact. After water has infiltrated the repository level, it must move down through approximately one thousand more feet of unsaturated rock to reach the saturated zone. Only from this zone can water be pumped to the surface.
Earthquake activity. Southern Nevada has low to moderate seismic activity. Experts have analyzed potentially active faults within sixty miles of Yucca Mountain. Although scientists expect earthquakes to occur at or near the mountain, those working on the design of the Yucca Mountain repository think that with modern techniques, repository facilities can be designed and constructed to withstand the effects of earthquakes and other natural phenomena. Contributing to underground safety is the fact that seismic ground motion diminishes with depth, so earthquakes have less impact deep underground than they do on or near the surface.
Transportation. Some people fear that vehicles moving nuclear waste across the country could be subject to accidents or become a target for terrorists. Federal regulations require that transportation cask designs be certified to withstand a series of severe impacts and extreme conditions without leaking radioactive materials. The regulations also require that shipments be monitored and tracked by satellite twenty-hour hours a day and accompanied by trained escorts, who must report in regularly. Armed escorts would be required through heavily populated metropolitan areas.
Other Nations' Approaches. Some nations using nuclear power do not have economical sources of fresh uranium to make nuclear fuel. France and the United Kingdom, for example, reprocess their own spent nuclear fuel for a second usage; they also do reprocessing for other countries, such as Japan and Switzerland. Current techniques for reprocessing involve complex chemical and physical procedures and actually produce additional radioactive waste. Most nations with nuclear power intend to build their own geologic repositories.
Health and safety. For more than twenty years, scientists and engineers have gathered technical data about the rock in Yucca Mountain, water movement through it, expected earthquakes, and the potential for volcanic disturbance of the proposed repository. Applying advanced software and high-powered computers to these data, scientists have estimated radiation doses due to the repository for tens of thousands of years. The radiation protection standards set by the Environmental Protection Agency (EPA) require that the calculations estimate the likely level of radiation that the most exposed member of the public would receive from the repository for ten thousand years after its closure. The standards require that this hypothetical person be assumed to live about fifteen miles from the repository, to eat some foods grown with local groundwater, and to drink two liters of water per day drawn from the most concentrated plume of repository-caused contamination in the aquifer. The estimates indicate that, for at least ten thousand years, the level of repository-yielded radioactivity this hypothetical person would likely receive, through all potential exposure pathways, would be far below fifteen millirem per year, the radiation protection standard for public health and safety.
see also Cancer; Health, Human; Radioactive Waste; Waste, Transportation of.
board on radioactive waste management, national research council, national academy of sciences. (2001). disposition of high-level waste and spent nuclear fuel: the continuing societal and technical challenges. washington, d.c.: national academy press. also available from http://www.books.nap.edu/books.
international atomic energy agency. (2002). institutional framework for long term management of high level waste and/or spent nuclear fuel. (iaea-tecdoc-1323) vienna, austria: iaea press. also available from http://www.pub.iaea.org/mtcd.
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Donald J. Hanley